An HVAC humidifier is a device or system that is used to add moisture to the air in a home or other environment. The device works by taking in dry air from the environment and passing it over a wet surface or through a spray of water. The water evaporates into the air and increases the humidity of the air in the environment. This is beneficial for many reasons, including increasing the comfort of the occupants, reducing dust and allergens in the air, and helping to protect wood furniture and floors from cracking or warping due to dry air. Additionally, a properly functioning HVAC humidifier can help reduce energy costs as it allows the HVAC system to operate more efficiently.
When the condition of the air entering a spray washer is humid, it can be expected to be humidified. However, if the spray is cooler than the air and the dew point, the vapour pressure of the spray will be lower than that of the moisture in the air and some moisture will be transferred into the spray water – resulting in dehumidification.
Spray washers are used to take out some of the dirt particles in the air, and the water pressure is usually between 200 and 300kPa, with the air velocity ranging from 2 to 2.5 m/s. To keep them clean and bacteria-free, these washers need to be regularly cleaned and treated, and their water quality must be supervised and recorded. Due to the numerous cases of Legionnaires’ disease caused by air conditioning systems, the Health and Safety Executive has singled out spray washers as a potential danger to health.
Modern air-processing systems may incorporate steam injection humidifiers, but these shouldn’t be positioned right after the cooling coil. At this point, the air will likely be near the point of saturation (100% RH) and unable to absorb any more moisture. Thus, it’s better to inject the super-heated, dry steam at over 200°C into the air close to its final release.
Humudifier Applications
Humidifiers are used in a variety of applications, including residential and commercial settings, such as homes, offices, hospitals, schools, and factories. In residential settings, humidifiers are used to improve air quality, provide relief from dry air, and reduce static electricity. In commercial settings, they are used to maintain optimal levels of humidity for workers, products, and processes. Humidifiers can also be used in industrial settings to prevent corrosion and improve productivity.
Types of HVAC Humidifiers
There are two primary types of HVAC humidifiers: evaporative and steam. Evaporative humidifiers use a wick and fan system to absorb water from a reservoir, and then blow it into the air. Steam humidifiers use an electric heating element to boil water and then blow the resulting steam into the air. Both types of humidifiers have their own benefits and drawbacks, so it is important to consider the particular needs of the space before selecting an appropriate humidifier.
Humidifier Types Comparison
| Type | Operating Principle | Moisture Output | Energy Efficiency | Maintenance Requirements | Initial Cost | Operating Cost |
|---|---|---|---|---|---|---|
| Bypass Flow | Uses HVAC system airflow through water panel | 3-11 gallons/day | High | Medium (panel replacement) | Low | Low |
| Fan-Powered | Integrated fan pushes air through water panel | 6-18 gallons/day | Medium | Medium (panel replacement) | Medium | Medium |
| Steam | Electrically boils water to create steam | 13-35 gallons/day | Low | Low-Medium | High | High |
| Ultrasonic | High-frequency vibrations create water droplets | 1-4 gallons/day | Very High | High (cleaning) | Medium-High | Very Low |
| Spray/Atomizing | Pressurized nozzles create fine water mist | 5-100+ gallons/day | High | High (nozzle maintenance) | High | Low-Medium |
| Evaporative Pad | Water drips through media as air passes | 3-12 gallons/day | Medium-High | Medium-High (pad replacement) | Low-Medium | Low |
| Electrode Canister | Electrical current between electrodes boils water | 5-30 gallons/day | Low | High (canister replacement) | Medium | High |
HVAC Humidifier Selection and Sizing
The selection of the correct humidifier for an HVAC system depends on a variety of factors, including the size of the building, the climate, the amount of humidity desired, and the type of HVAC system. Each type of humidifier has its own advantages and disadvantages. In some cases, the installation of multiple types of humidifiers may be necessary to achieve the desired humidity level.
Humidity Control Parameters by Application
| Application | Recommended RH Range | Critical Control Points | Monitoring Requirements | Common Issues | Recommended Humidifier Type |
|---|---|---|---|---|---|
| Data Centers | 40-60% | ±5% RH | Continuous with alerting | Electrostatic discharge, equipment failure | Steam, Ultrasonic |
| Healthcare Facilities | 30-60% | ±3% RH | Continuous with logging | Bacterial growth, patient comfort | Steam (isothermal) |
| Residential | 30-50% | ±10% RH | Basic controller | Window condensation, comfort | Bypass, Fan-Powered |
| Museums/Archives | 45-55% | ±2% RH | Continuous with logging | Material degradation | Steam, Ultrasonic |
| Manufacturing | 40-60% | Application-specific | Process integration | Product quality, static discharge | Spray, Steam |
| Printing Facilities | 50-60% | ±3% RH | Continuous | Paper wrinkling, misalignment | Spray, Steam |
| Wood Processing | 40-55% | ±5% RH | Regular | Material warping, cracking | Spray, Evaporative |
| Laboratories | 45-55% | ±2% RH | Continuous with alerting | Test reliability, equipment accuracy | Steam, Ultrasonic |
Once the appropriate type of humidifier has been selected, it is important to ensure that the size of the humidifier is appropriate for the size of the building. Generally, a larger humidifier is recommended for larger buildings, as it will be able to provide more humidity to the air. However, it is possible to use a smaller humidifier in a larger building if the humidity level needs to be kept at a lower level. It is important to consult a professional to ensure the correct size is selected.
The following steps should be taken to ensure proper sizing when selecting a humidifier for an HVAC system:
1. Determine the air flow rate of the system.
2. Calculate the desired humidity level.
3. Calculate the total humidity requirement.
4. Determine the air velocity over the humidifier.
5. Select the appropriate humidifier size based on the total humidity requirement.
6. Calculate the humidifier’s energy consumption.
7. Select a humidifier that is capable of meeting the energy requirements.
8. Consider any additional features needed for the system.
Humidifier Sizing Factors
| Building Type | Moisture Load Factors | Calculation Variables | Typical Capacity (lbs/hr per 1000 ft²) | Air Changes Consideration |
|---|---|---|---|---|
| Residential | Occupants, cooking, bathing, infiltration | Volume, construction type, occupants | 0.5-2 | 0.5-1 ACH |
| Commercial Office | Occupants, equipment, infiltration | Floor area, occupant density, ventilation rate | 1-3 | 1-2 ACH |
| Hospital | Occupants, medical equipment, ventilation | Department type, bed count, ventilation rate | 3-8 | 6-15 ACH |
| Museum | Material preservation, visitors | Collection type, volume, building envelope | 2-5 | 1-4 ACH |
| Industrial | Process requirements, air exchanges | Process type, equipment loads, exhaust rates | 5-20+ | 2-60 ACH |
| Data Center | Equipment cooling, ventilation | IT load, cooling approach, ventilation strategy | 1-4 | 1-4 ACH |
Water Quality Requirements by Humidifier Type
| Humidifier Type | Recommended Water Type | TDS Tolerance (ppm) | Hardness Tolerance (gpg) | Filtration Requirements | Maintenance Impact of Poor Water Quality |
|---|---|---|---|---|---|
| Steam (Electrode) | Tap water | 125-1250 | 3-12 | Basic filtration | Shortened canister life, reduced output |
| Steam (Resistive) | Treated/DI water | <50 | <1 | RO or DI system | Element scaling, reduced output |
| Ultrasonic | Demineralized | <5 | <0.5 | RO or DI system | White dust, clogged transducers |
| Evaporative | Tap water | <400 | <10 | Basic filtration | Media scaling, reduced efficiency |
| Atomizing/Spray | Treated water | <100 | <3 | Multi-stage filtration | Nozzle clogging, mineral deposits |
| Centrifugal | Treated water | <200 | <5 | Basic filtration | Impeller scaling, reduced output |
Energy Consumption Comparison
| Humidifier Type | Capacity Range (lbs/hr) | Energy Input (kW) per lb/hr | Annual Energy Cost* | Payback Period vs. Electrode Steam | CO₂ Emissions (kg/yr)** |
|---|---|---|---|---|---|
| Electrode Steam | 5-300 | 0.33-0.35 | $$$$ | Baseline | 2,800-3,000 |
| Resistive Steam | 2-250 | 0.31-0.33 | $$$$ | 3-5 years | 2,600-2,800 |
| Gas-Fired Steam | 50-3000 | 0.12-0.15 | $$ | 1-3 years | 1,800-2,200 |
| Ultrasonic | 2-40 | 0.02-0.04 | $ | 1-2 years | 170-340 |
| High-Pressure Atomization | 10-1200 | 0.005-0.02 | $ | 1-3 years | 40-170 |
| Evaporative | 5-500 | 0.01-0.03 | $ | 2-4 years | 85-255 |
*Based on 2,500 operating hours/year and average utility rates of $0.15/kWh and $0.80/therm
**Based on 0.85 kg CO₂/kWh for electricity and 0.2 kg CO₂/kWh equivalent for natural gas
Humidifier Control Integration
| Control Type | Accuracy | Response Time | Integration Complexity | Compatible Systems | Typical Applications |
|---|---|---|---|---|---|
| On/Off | ±10% RH | Slow | Low | Basic HVAC | Residential, Small Office |
| Proportional | ±5% RH | Medium | Medium | BMS, DDC | Commercial, Light Industrial |
| PID | ±2% RH | Fast | High | BMS, DDC, PLC | Critical Environments, Healthcare |
| BACnet/Modbus | ±2-5% RH | Fast | Medium-High | Modern BMS | Commercial, Institutional |
| IoT-Enabled | ±3-8% RH | Medium-Fast | Medium | Cloud Systems | Smart Buildings, Remote Monitoring |
| Dew Point Control | ±1-3% RH | Fast | High | Advanced BMS | Critical Manufacturing, Labs |
Legionella Risk and Prevention by Humidifier Type
| Humidifier Type | Inherent Risk Level | Water Temperature Range | Required Prevention Measures | Maintenance Frequency | Recommended Treatments |
|---|---|---|---|---|---|
| Steam | Very Low | >100°C | Standard water treatment | Quarterly | Periodic draining |
| Ultrasonic | Medium-High | 10-30°C | Regular disinfection, water treatment | Weekly-Monthly | UV, Silver ion, Biocides |
| Spray/Atomizing | High | 10-30°C | Continuous treatment, regular cleaning | Weekly | UV, Chemical biocides, Regular draining |
| Evaporative | Medium | 10-35°C | Regular media replacement, water treatment | Monthly | Biocides, Regular draining |
| Air Washer | Very High | 15-35°C | Comprehensive water management plan | Weekly | Chemical biocides, UV, Regular cleaning |
Global Humidifier Manufacturers Comparison
| Manufacturer | Specialization | Technology Focus | Market Segment | Geographic Presence | Notable Features |
|---|---|---|---|---|---|
| Condair | Comprehensive | All technologies | All segments | Global | Integrated controllers, energy optimization |
| Carel | Control systems | Electronic steam, adiabatic | Commercial, Industrial | Global | BMS integration, IoT connectivity |
| Nortec | Steam systems | Electrode, resistive steam | Commercial, Healthcare | North America, Europe | Hygiene-certified models |
| DriSteem | Steam systems | Gas-fired, electric | Institutional, Industrial | North America, Europe | High-capacity systems |
| Armstrong | Industrial systems | Direct steam injection | Industrial | Global | Process integration |
| Neptronic | Electronic control | Steam, evaporative | Commercial, Industrial | North America, Europe | BACnet/Modbus native |
| Honeywell | Residential | Bypass, fan-powered | Residential | Global | Smart home integration |
| Aprilaire | Residential | Bypass, steam | Residential, Light Commercial | North America | IAQ system integration |
| Stulz | Data centers | Adiabatic, ultrasonic | IT, Precision cooling | Global | Energy-efficient designs |
| Munters | Desiccant systems | Evaporative, spray | Industrial | Global | Process-specific solutions |
